Organic Chemistry 1 Lab Report

1. Percent recovery is defined as the calculated percentage of an original compound after the completion of a chemical reaction. For instance, purification reactions such as recrystallization reactions are eligible to calculate percent recovery of the substance of the reaction since the substance at the end of the chemical reaction remains unchanged. The value obtained for percent recovery may not be exact due to any spillage that may occur before the final product of the crystallization reaction. (1) Percent recovery formula: Percent recovery = amount of substance recovered on purification amount of substance originally taken !´ !100 (1) Percent yield is defined as the percent ration of the actual yield – amount of product obtained from a chemical reaction- to the theoretical value - amount of product obtained from the stoichiometric or balanced equation, using the limiting reactant to determine product- multiplied by a hundred. If the actual and theoretical. If the actual and theoretical yield are the same, the percent yield is 100%. It is usually lower than 100% because the actual yield is usually lower due to incomplete reactions or loss of sample during reaction. (2) Percent yield formula: actual yield theoretical yield ´ 100 (2) The difference between percent yield and percent recovery is that yield measures the efficiency of the extracted product compared to a literature value whereas percent recovery compares the amount of product collected when compared to its original value. In experiment 1, percent recovery is used for crystallization Mass of unknown N collected initially = 1.01 g Mass of unknown N (Caffeine) solid purified = 0.36 g Percent recovery = amount of substance recovered on purification(g) amount of substance originally taken(g) ! ´ !100 $.&' Percent recovery = (.$(! ´ !100= 35.64% In experiment 2, percent recovery is used for distillation Volume of unknown number 4 (Acetone) = 20.0 mL Volume collected = 13.0 mL Percent recovery = amount of substance recovered (mL) amount of substance originally taken+(mL) !´ !100 (&.$+,Percent recovery = .$.$+,/! ´ !100= 65.0% 2. a) The R 0 value is the ratio of distance traveled from origin (x) to the distance the solvent has traveled (y). (3) 1 $.'$ In the TLC plate shown below, an example application of R 0= 2 = &.&$= 0.18 This low R 0 !value indicates a strong attraction of the compound with the stationary phase and the compound indicates high polarity. The R 0 value indicates polarity and not the purity of the chemical. (3) Since the 3 visual spots were seen at the exact same distance x just barely above the line this indicates N is very polar and that the suspect was not contaminated. (3) Figure 1. TLC plate of experiment 1 (Chem draw) b) In the current TLC experiment the eluent used is ethanol. Ethanol is a very polar molecule due to its hydroxyl (OH) group, with the high electronegativity of oxygen allowing hydrogen bonding to take place with other molecules. Ethanol therefore attracts polar and ionic molecules. (4) Ethanol is considered to be more polar than ethyl acetate and thus polar solvent would be highly attracted to the adsorbant and would move up the plate more slowly. When a solvent is changed to ethanol the polarity of the solvent would bind to the silica gel before the analyte which causes the analyte to travel across the silica gel further up resulting in higher 𝑅3 values. Since the analyte in this experiment is caffeine the spots are found near the stationary phase since caffeine is a highly polar molecule. Therefore, the R 0 is considered to be somewhat low at 0.18. (3) 3. Experiment 1: Purification of Unknown N Unknown N 5 237.5 C Caffeine Mixed melting point 235.0-237 C 235.0-238.1 C of Unknown N & Ethanol 𝐑𝐟 Unknown N 0.18 Eluent: Ethanol Co-spot 0.18,0.18 Plate: silica Caffeine 0.18 Visualization method: UV The unknown N was found to be caffeine in the first part of the experiment since the experimental melting point was very close to the literature range. Moreover, the second part of the experiment confirmed that the unknown solid is indeed caffeine as the R 0 value of the unknown as well as the co-spot – unknown N + Caffeine- and Caffeine were all 0.18. All the spots on the TLC plate travelled across the plate along the same distance 0.60 cm just barely above the origin line. (3) Because the spots were found to be ideally on the same line and since the R 0 values were equal, we can conclude that there was no contamination. The TLC plate shown above indicates that there are no impurities because there is only one spot present per column. (3) Experiment 2: Distillation of a Liquid Unknown 4 Unknown 4 54 C Acetone 56 C 6 Isopropyl 81-83 C 7 3590 Very strong, Very broad O-H 1708 Strong C O 1364 medium O-H 1224 Strong C-O During the distillation part of experiment 2, the suspected identity was found to be acetone due to the experimental boiling point being near the literature value. When the thermometer read 45 C, drops started appearing and the temperature continued to increase until the thermometer read 54 C. At 54 C the dripping rate was steady, this indicates that the solution plateaued and that the liquid solution is turning into gas. The temperature fluctuated between 5054 C. Eventually, the liquid exceeds its boiling point and begins evaporating giving off a pure distillate. Distillation is completed when the temperature rises above the plateau. Volume of distillate collected was 9.8 mL. (3) Infrared spectroscopy (IR) measures what wavenumbers the molecule absorbs and by examining the IR spectrum of a compound, the functional groups of that sample can be determined. (3) The main functional group in acetone is the carbonyl group which is found at 1708 cm5( . The very broad band of O-H, wavelength 3590 cm5( , found at the beginning of the spectrum is due to the contamination of the sample with water molecules. While disassembling the distillation apparatus, the water knob was accidentally rotated to increase water pressure flowing into the apparatus which caused some leakage of water into the purified sample. (3) Figure 2. IR spectrum of Acetone 4. Common knowledge is knowledge that is known to the reader and the writer according to specific context. In this second level Organic Chemistry course, certain information must be known to both the students and the instructors. For instance, in experiment 1 the definition of a melting point – the temperature at which a solid melts - is considered common knowledge. The terms solvent, solute and solution are also considered common knowledge at this level. Information that is required to be extracted and precise must be cited. Such information is not considered common knowledge and are considered to be facts. In experiment one, literature values of melting points of the organic compounds and their physical data must be cited, as they are not common knowledge. (3) 6. a) Figure 3. Screenshot of performed search for Unknown I b) The identity of unknown I is benzophenone. c) Rhombic prisms (stable form); monoclinic prisms (labile form) with apricot-peach taste d) Department of Chemistry, Purdue University, Lafayette, Indiana 47907, U.S.A.